12V Batteries Question

**sande005** · 02-15-2022, 07:01 AM

I've advocated for this in several earlier threads, with charts. You don't need to wrestle them in and out of the RV when not in use. Just make sure:

1. They have been verified not to be low on water.
2. They are fully charged (give them 24 hrs with the RV plugged in and the switch on).
3. When not using, they are fully disconnected. Don't trust the switch, take one set of wires off of one of the terminals.

They can go many, many months (8-12) without attention. The exception would be in extremely hot weather for long periods (all summer in Arizona, etc.).
Fully charged batteries will not freeze until they get to -74F.

See my earlier posts for more info about "how long at what average temperature".

**powerscol** · 02-15-2022, 09:22 PM

Rule of thumb. When you can remove the red key the battery disconnect is off there will be no power to the trailer except for parasitic draws. That's why you need to pull a battery cable (negative) to actually isolate the batterys for storage. If the disconnect key is in (on) and can't be removed the batterys are connected to the trailer. I never mess with the disconnect key and just pull the negative cables off the batterys.

**Jerryr** · 02-15-2022, 09:32 PM

I installed a high quality real disconnect switch as have others. This eliminates having to remove a cable from the battery.

Switch https://www.amazon.com/gp/product/B000MMC914/

Cables https://www.amazon.com/gp/product/B07BXXNMBJ/

**Hoopy Frood** · 02-16-2022, 07:13 AM

Before you go through the hassle of installing an OEM Battery Disconnect Switch, or pulling the negative battery cable, check the draw from the battery when the factory Battery Disconnect Switch is "OFF". Some of them, mine included, actually cut all power draws.

**RV Sailor** · 02-19-2022, 03:58 PM

=sande005;414912]I've advocated for this in several earlier threads, with charts. You don't need to wrestle them in and out of the RV when not in use. Just make sure:

1. They have been verified not to be low on water.
2. They are fully charged (give them 24 hrs with the RV plugged in and the switch on).
3. When not using, they are fully disconnected. Don't trust the switch, take one set of wires off of one of the terminals.

They can go many, many months (8-12) without attention. The exception would be in extremely hot weather for long periods (all summer in Arizona, etc.).
Fully charged batteries will not freeze until they get to -74F.

See my earlier posts for more info about "how long at what average temperature".[/QUOTE]

Sorry I could not disagree more with this practice of just letting them go after disconnecting

Batteries have a normal discharge rate when charge is not applied when just sitting there not connected. Wet cells being the greatest.
Letting a battery sit in a state of decreasing charge will led to at the very least premature Lessing of its life. Batteries “ learn “ their charge too.

If the maximum you charge a battery is less than its theoretical capability charge it will eventually lower its capability. That’s why it’s important to either trickle charge them or run a true charge through them monthly to bring them up to their full potential. Some who doesn’t practice this procedure will never be able to quantify or even notice their loss but almost all knowledgeable people who depend on their batteries know that recharging them to their potential as often as possible is important.

The one exception are the lithiums where you do get penalized by not bringing the battery back to full charge.

**sande005** · 02-20-2022, 07:43 AM

Originally Posted by RV Sailor

Sorry I could not disagree more with this practice of just letting them go after disconnecting

Batteries have a normal discharge rate when charge is not applied when just sitting there not connected. Wet cells being the greatest.
Letting a battery sit in a state of decreasing charge will led to at the very least premature Lessing of its life. Batteries “ learn “ their charge too.

If the maximum you charge a battery is less than its theoretical capability charge it will eventually lower its capability. That’s why it’s important to either trickle charge them or run a true charge through them monthly to bring them up to their full potential. Some who doesn’t practice this procedure will never be able to quantify or even notice their loss but almost all knowledgeable people who depend on their batteries know that recharging them to their potential as often as possible is important.

The one exception are the lithiums where you do get penalized by not bringing the battery back to full charge.

It is unfortunate that there is so much out there that is contradictory about maintaining lead acid batteries. You base your feeding and care on what you have found out, me on what I have found.
To my points:
Yes, they definitely discharge themselves over time. But it is very temperature dependent, the warmer the faster. Actual controlled testing vs oft repeated "rules of thumb" is out there, but harder to find. In my case, over several decades with the 6 various batteries I have to care for, they have never been below 90% charge after 6 mos. of unattended outdoor storage. The only one I ever had to replace in less than 5 years was one that accidentally discharged to zero, and left it that way for over a week (in the summer). A couple I am currently really pushing - this will be their 12th year. But I would be more attentive as the average storage temp goes up - outdoors in Minn, over the winter is great. Arizona in the summer is bad.

Lead Acids do NOT suffer from memory effects. Ever. Google "do lead acid batteries develop memory" and all the results are from multiple manufacturers stating that they do NOT have this problem.

Yes, it is bad to store them at partial charge, but unanswered is "how partial"? My experience and that of thousands of boat owners who store boats over the winter in my area points to little accelerated degradation over time. Again, much warmer climates likely are different. Only you can decide where your cutoff is that requires greater care and feeding. For me, not getting below 90% counts as pretty much fully charged.

How much trade-off is one willing to make to potentially extend their life? For me, with six, uninstalling/reinstalling is a major feat. And needing the added storage space, electrical access, charging devices, etc. is very problematic. One Group 27 battery is much less of an issue than 2 grp 31 AGMS, 2 6v, etc.
Is the cost/hassle worth the trade off for whatever fractional addition to their life span? For me, if they "only" last 5-6 years, instead possibly going 6-7, that is a fair trade-off for the convenience. But after 20 years, that "trade" appears not to be needed, and I have won in the battery arena.

Now, all of the above pre-supposes otherwise good care. Never letting the electrolyte get low. Always keeping them fully charged during the active season. Using a quality charger. Never over charging. Never discharging to low/very low levels, or at least staying low for any length of time. Or (as I found) never letting them go completely dead.

On other topics:
I don't understand your lithium comment. While the issue is minor, if one is looking for ultimate maximum life out of lithiums, they should be stored at a partial discharge level. But the reality is that LiFe's are really stable, so any gain is pretty minimal.
And then there is the old "store them on wood, not concrete" myth that was brought up in another post.....

**RV Sailor** · 02-20-2022, 09:07 AM

Thanks for the detailed explanation. However like I said before , recommending leaving a lead acid battery ( not lithium)not close to charge for extended periods of time, is not a good practice.

My answer is not based on feeling as you implied , but on factual actual personal anecdotal evidence not on some cut and paste internet research.

I am glad you mentioned your boater friends. I in fact have a 35 ft sailboat and have had Haleakula for over 30 years. Because we take extensive trips of over 1500 miles she requires a good knowledge of not only 12 volt systems but battery chemistry and maintenance care as well. We have gone from wet cells , to advanced Lifeline AGM to Oasis Firefly to Lithium over the years.

Our current sailboat and Imagine 2500RL has lithiums, 500/ 750 watt solar, sophisticated Victron Multiplex inverter chargers . I kinda understand batteries and 12 volt through 40 years experience but even then my best friend is a marine electrician who continues to educate me in this rapidly changing field.

Batteries have memory and limits. You can program a battery memory so that you lower its potential charge by not bringing it up to charge. As I mentioned ALL types except lithium and a specialized carbon fiber AGM called Oasis Firefly. If you leave your lead acid batteries at a less than 100% charge for long periods of time, ( like over the winter or 6-8 months) like you advocated without charging them , the will fully charged figure will be lower ed from its initial full charge capacity capability by your misuse. Lithiums , as I mentioned , you are not penalized in that matter.

There is a reason almost 100% of the people I know to either trickle charge their batteries or charge them full during the down months they may be sitting. These people don’t do it to waste their time, it’s just good maintainence and SOP.

To the OP , continue to remove your batteries and just trickle or real charge them. The will last longer and you will get the most life out of them at the best charge. Batteries / Electrical is one of the most expensive and least understood parts of RV and sailboats. I commend you for your interest in gaining knowledge in that area

Originally Posted by sande005

It is unfortunate that there is so much out there that is contradictory about maintaining lead acid batteries. You base your feeding and care on what you have found out, me on what I have found.
To my points:
Yes, they definitely discharge themselves over time. But it is very temperature dependent, the warmer the faster. Actual controlled testing vs oft repeated "rules of thumb" is out there, but harder to find. In my case, over several decades with the 6 various batteries I have to care for, they have never been below 90% charge after 6 mos. of unattended outdoor storage. The only one I ever had to replace in less than 5 years was one that accidentally discharged to zero, and left it that way for over a week (in the summer). A couple I am currently really pushing - this will be their 12th year. But I would be more attentive as the average storage temp goes up - outdoors in Minn, over the winter is great. Arizona in the summer is bad.

Lead Acids do NOT suffer from memory effects. Ever. Google "do lead acid batteries develop memory" and all the results are from multiple manufacturers stating that they do NOT have this problem.

Yes, it is bad to store them at partial charge, but unanswered is "how partial"? My experience and that of thousands of boat owners who store boats over the winter in my area points to little accelerated degradation over time. Again, much warmer climates likely are different. Only you can decide where your cutoff is that requires greater care and feeding. For me, not getting below 90% counts as pretty much fully charged.

How much trade-off is one willing to make to potentially extend their life? For me, with six, uninstalling/reinstalling is a major feat. And needing the added storage space, electrical access, charging devices, etc. is very problematic. One Group 27 battery is much less of an issue than 2 grp 31 AGMS, 2 6v, etc.
Is the cost/hassle worth the trade off for whatever fractional addition to their life span? For me, if they "only" last 5-6 years, instead possibly going 6-7, that is a fair trade-off for the convenience. But after 20 years, that "trade" appears not to be needed, and I have won in the battery arena.

Now, all of the above pre-supposes otherwise good care. Never letting the electrolyte get low. Always keeping them fully charged during the active season. Using a quality charger. Never over charging. Never discharging to low/very low levels, or at least staying low for any length of time. Or (as I found) never letting them go completely dead.

On other topics:
I don't understand your lithium comment. While the issue is minor, if one is looking for ultimate maximum life out of lithiums, they should be stored at a partial discharge level. But the reality is that LiFe's are really stable, so any gain is pretty minimal.
And then there is the old "store them on wood, not concrete" myth that was brought up in another post.....

**mbergthold** · 02-21-2022, 12:33 PM

I remove both batteries, place on 2x8 in garage, and connect a "battery minder"

**RV Sailor** · 02-21-2022, 01:50 PM

Perfect 😄😄😄😄😄

Originally Posted by mbergthold

I remove both batteries, place on 2x8 in garage, and connect a "battery minder"

**goducks14** · 02-21-2022, 02:48 PM

Contrary to mythical belief LA batteries can be set directly on concrete.

Difference Between Concrete and Cement)

But don’t take our word for it. To quote Interstate Batteries, “The type of plastic (polypropylene) used in battery cases is a great electrical insulator. Also, tremendous technological improvements have been made in the seals around the battery posts and vent systems, which have virtually eliminated electrolyte seepage and migration. So, it’s OK to set or store your battery on concrete.”

This leads us to another common car battery myth- that cold weather will increase this self-discharge rate. In fact, the opposite is true- cold weather slows the self-discharge (slower chemical reactions) and hot weather speeds it up (faster chemical reactions). As Pacific Power Batteries notes, “A battery stored at 95° F (35° C) will self-discharge twice as fast than one stored at 75° F (23.9° C).”